Many thunderstorm climatologies use surface and upper air observations to discriminate ES from SS. Again there is concern too few identified Australian ES events would result from observations-based discriminators. As an alternative to sparse surface and upper air observations, the ECMWF Era Interim Reanalysis (hereafter referred to as EraInt) does have finer spatial resolution (spatial information on a 0.75 degrees x 0.75 degrees grid), however the vertical and temporal resolution is courser ( 37 vertical levels, 6 hour temporal resolution). Like other model-based reanalyses, EraInt contains biases. Bao and Zhang (2013) compared 3000 observed soundings from the Tibetan Plateau, a region where observed soundings are excluded from EraInt reanalysis, thus EraInt are independent of observed soundings. Large moist mean biases through lowest 300hPa depth were found (relative humidity +10 to +25% above observed), along with small low level low level cool mean biases (-0.25 to -1.5 degrees Celsius). To investigate if these same mean biases occur in Australia, observed and EraInt soundings at 2 sites (one coastal and one inland) for one year will be compared.

Despite EraInt reanalysis low level moist and cool biases shown by Bao and Zhang (2013), Allen and Karoly (2013) found EraInt surface mixed-layer (50mb depth) CAPE over Australia compared well to 7 years of observed soundings with only small positive biases, whereas EraInt mixed-layer convective inhibition (CIN) was underestimated compared to observations. CAPE, CIN, and other quantities have been used as discriminator components to derive other ES and SS climatologies (a representation of different discriminators are summarised in Table 1. Allen and Karoly’s results suggest EraInt could be used to calculate the near-storm discriminators in Table 1 and construct a climatology ES and SS events, provided discriminators quantities such as MUCAPE, CIN and θe compare well to observed sounding derived MUCAPE, CIN, θe discriminator quantities. This comparison can be performed using observed and EraInt thunderstorm soundings rather than all soundings to reduce the number of zero instability quantity calculations. For accurate comparison of discriminator quantities, observed soundings will be reduced in vertical resolution to EraInt pressure levels, whilst EraInt soundings will be capped at observed sounding vertical extents. Thunderstorm soundings with GPATS lightning within +- 1 hour and +-0.25 degrees latitude and longitude of the sounding location, could be appropriate spatial and temporal windows given similar choices by Thompson et. al. 2003 (soundings within 40km radius and +-3min of thunderstorm reports).